Various industries, including the paper and pulp industries and food processing industries by way of non-limiting example, involve the generation of undesirable foam within and on the processing line. Left uncontrolled, this foam can accumulate uncontrollably and eventually shut down a processing line. A typical industry solution involves the addition of chemical de-foaming or anti-foaming agents to a liquid (e.g., water) associated with the industrial process in question. Although chemical additives have proven effective in controlling unwanted foam accumulation, effective non-chemical methods and solutions have been sought. Two reasons for avoiding chemical additives are cost and safety. Safety is a particular concern in industrial food processing settings because measure must be taken to ensure that levels of chemicals coming in contact with the food and reaming thereon after processing are acceptably low.
Typically the composition of built-up foam transitions from a ‘wet foam’ at the bottom of the foam (small bubble structure with water-like flow ability) to a ‘dry foam’ at the surface (large bubbles that adhere to all surfaces and resist flow). Once a significant foam build-up has accumulated, most of the foam volume consists of the drier foam. Several non-chemical approaches for foam control have been evaluated over the years. Some are currently utilized to a limited degree, but primarily to selectively augment chemical additives. There are primarily three basic non-chemical approaches for foam control: (1) water spray, (2) optical, and (3) centrifugal, each of which is briefly described in turn.
Water sprays are sometimes used to partially “knock down” the foam by spraying the top-surface dry foam to condense it from dry foam to wet foam and thereby reduce the total volume. Large foam-control spray systems are sometimes used in waste treatment and aquaculture farms. The use of water-spray foam control is confined primarily to localized trouble areas, where, due to a combination of physical layout and/or turbulent water flow, foam generation is rapid. These local sprays can be effective; however, in many cases, these sprays, while reducing the foam volume at the point of impact, can create holes in the foam while pushing foam into the periphery of the spray impact area where it continues to grow. Even the condensed ‘wet foam’ can continue to grow unacceptably within the spray impact area, thus minimizing any further reduction in foam volume. The use of a sprays in these localized ‘hot spots’ does not address the foam problem on the entire production line where, due to the continuous agitation throughout a facility, the foam builds within vessels and tanks, for example.
Optical solutions for controlling foam have been proposed and selectively tested. In one such system, a high power laser is used to destroy foam. These lasers emit light at or near a wavelength at which the liquid has a strong absorption line. It is believed that the optical absorption by the liquid locally heats the surface of a bubble and causes its destruction. One implementation of this approach includes a CO2 laser mounted directly over a tank into which foam flows and where additional foam is also generated due to turbulence within the tank. The laser beam ‘writes’ a line across the foam in a continuously varying pattern. The line defines a region in which the foam is destroyed and the underlying surface water is exposed. Rapid writing of the laser beam reduces the foam volume in those regions and further inhibits foam growth because it provides a localized “non-foamed” region which the surrounding foam fills, thus reducing the rate of foam growth in surrounding regions of the tank. Cost is a primary factor restricting the commercial deployment of such systems. The combination of the systems' capital costs and theft operating costs, especially for deployment on a distributed processing line, is widely considered prohibitive.
Centrifugal systems have been used successfully for many years in a variety of industries and applications for separating the constituent liquids and gases of mixtures consisting of liquids and gases. Centrifugal gas/liquid separators typically rotate the liquid itself creating a cyclone or vortex within the liquid. As the “mixed medium” is rotated, the higher-density liquid is driven to the outside leaving behind on the inside the less dense gas, which can be subsequently removed.
Since foam is a gas/liquid mixture of, for example, air and water, a centrifugal gas/liquid separator can be a reasonable approach for non-chemical de-foaming. Consequently, variations of this technology have been studied and have resulted in designs, patents, and products directed at de-foaming applications. For the most part, air/gas separators are complicated systems, all of which require some subset of not only the means for high speed water rotation, but also vacuum systems, pumps, multi-stage impellers, filtering systems, and even heat. These systems do not lend themselves to in-situ foam control, but are best operated as an off-line system where the foamy solution needs to be pulled from all the key areas of the product-flow line into the separator(s), filtered, de-foamed, and then carefully pumped back into the line so as not to generate additional foam. Thus, the current separators manifest themselves as additional stand-alone closed operating systems. The costs associated with these systems are high and include capital cost, installation, maintenance, and floor space.
Other de-foaming technologies exist, but for very specialized applications, such as the aeration/separation systems used in aqua/fish farming. Similar to the application mismatches described above, these are large systems utilizing aeration, pumping and evacuation techniques. Ultrasonic solutions have also been proposed, and have found specialized applications, such as in canning operations, but have similarly proved not to be a good general fit for broad applications.
Accordingly, a need exists for a cost effective, chemical-free foam control system and method that lends itself to broad implementation across various industries challenged by undesirable foam generation.